Re: Questions...
No headphone jack. OnePlus canned the 3.5mm jack as of the OnePlus 6T. I've spent the intervening two years acquiring USB-C to 3.5mm adapters every six months or so when I've forgotten to pack one of the bloody things.
More annoyingly, none of the phones come with a dedicated adapter to allow you to charge the phone as well as listen to music on wired headphones at the same time. OnePlus doesn't make such an adapter, and the third party adapters are very much hit and miss.